MDEV-27027 Atomic DDL: Assertion failed upon unsuccessful multi-RENAME TABLE

When executing an atomic sequence of RENAME operations, such as:
    RENAME TABLE t1 TO t2, t3 TO t4, ...
any failure in the sequence triggers a rollback of previously completed
renames to preserve atomicity.

However, when an error occurs, `my_error()` is invoked immediately, which
sets the `thd->is_error()` flag. This premature flag setting causes
the rollback logic to misinterpret the thread state, leading to incorrect
reversion behavior and assertion failures.

To address this, the errors are now not emitted immediately but captured
and postponed. A new class `Postponed_error_handler` is introduced for
this purpose. Only after all operations are completed (including
possible DDL reversion), the captured errors are emitted.

Author: Olernov

mysql-test/main/rename.result

@@ -173,3 +173,43 @@ drop table t2;
 rename table if exists t1 to t2;
 alter table if exists t2 rename to t1;
 drop table t1;
+#
+# MDEV-27027 Atomic DDL: Assertion `!param->got_error' failed upon
+#             unsuccessful multi-RENAME TABLE
+#
+CREATE TABLE t1 (a INT);
+CREATE TRIGGER tr1 AFTER INSERT ON t1 FOR EACH ROW
+INSERT INTO db.t SELECT SLEEP(0.05);
+# Missing table in RENAME TABLE (should error)
+RENAME TABLE t1 TO t2,
+missing1 TO m1;
+ERROR 42S02: Table 'test.missing1' doesn't exist
+SHOW CREATE TRIGGER tr1;
+Trigger	sql_mode	SQL Original Statement	character_set_client	collation_connection	Database Collation	Created
+tr1	STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION	CREATE DEFINER=`root`@`localhost` TRIGGER tr1 AFTER INSERT ON `t1` FOR EACH ROW
+INSERT INTO db.t SELECT SLEEP(0.05)	latin1	latin1_swedish_ci	latin1_swedish_ci	#
+CREATE TABLE t2 (a INT);
+# Attempt to rename to existing table (should error)
+RENAME TABLE t2 TO t3,
+t1 TO t3;
+ERROR 42S01: Table 't3' already exists
+SHOW CREATE TRIGGER tr1;
+Trigger	sql_mode	SQL Original Statement	character_set_client	collation_connection	Database Collation	Created
+tr1	STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION	CREATE DEFINER=`root`@`localhost` TRIGGER tr1 AFTER INSERT ON `t1` FOR EACH ROW
+INSERT INTO db.t SELECT SLEEP(0.05)	latin1	latin1_swedish_ci	latin1_swedish_ci	#
+# Test multiple warnings captured during renaming
+RENAME TABLE IF EXISTS
+missing1 TO m1,
+missing2 TO m2,
+t2 TO t3,  # this rename succeeds
+missing3 TO m3;
+Warnings:
+Note	1146	Table 'test.missing1' doesn't exist
+Note	1146	Table 'test.missing2' doesn't exist
+Note	1146	Table 'test.missing3' doesn't exist
+RENAME TABLE IF EXISTS
+missing1 TO m1,
+t1 TO t3,  # this will error: table exists
+missing2 TO m2;
+ERROR 42S01: Table 't3' already exists
+DROP TABLE t1, t3;

mysql-test/main/rename.test

@@ -166,3 +166,44 @@ drop table t2;
 rename table if exists t1 to t2;
 alter table if exists t2 rename to t1;
 drop table t1;
+
+--echo #
+--echo # MDEV-27027 Atomic DDL: Assertion `!param->got_error' failed upon
+--echo #             unsuccessful multi-RENAME TABLE
+--echo #
+CREATE TABLE t1 (a INT);
+CREATE TRIGGER tr1 AFTER INSERT ON t1 FOR EACH ROW
+  INSERT INTO db.t SELECT SLEEP(0.05);
+
+--echo # Missing table in RENAME TABLE (should error)
+--error ER_NO_SUCH_TABLE
+RENAME TABLE t1 TO t2,
+             missing1 TO m1; # this will error: missing table
+
+--replace_column 7 #
+SHOW CREATE TRIGGER tr1;
+
+CREATE TABLE t2 (a INT);
+
+--echo # Attempt to rename to existing table (should error)
+--error ER_TABLE_EXISTS_ERROR
+RENAME TABLE t2 TO t3,
+             t1 TO t3; # this will error: table exists
+
+--replace_column 7 #
+SHOW CREATE TRIGGER tr1;
+
+--echo # Test multiple warnings captured during renaming
+RENAME TABLE IF EXISTS
+  missing1 TO m1,
+  missing2 TO m2,
+  t2 TO t3,  # this rename succeeds
+  missing3 TO m3;
+
+--error ER_TABLE_EXISTS_ERROR
+RENAME TABLE IF EXISTS
+  missing1 TO m1,
+  t1 TO t3,  # this will error: table exists
+  missing2 TO m2;
+
+DROP TABLE t1, t3;

sql/sql_class.h

@@ -2047,6 +2047,76 @@ class Counting_error_handler : public Internal_error_handler
 };
 
 
+extern "C" void my_message_sql(uint error, const char *str, myf MyFlags);
+
+/**
+  Error handler that captures and postpones errors.
+  Warnings and notes are passed through to the next handler.
+  Stored errors can be re-emitted later via emit_errors().
+*/
+
+class Postponed_error_handler : public Internal_error_handler
+{
+  struct Error_entry
+  {
+    uint sql_errno;
+    char message[MYSQL_ERRMSG_SIZE];
+    Error_entry *next;
+  };
+
+  Error_entry *m_first;
+  Error_entry *m_last;
+  MEM_ROOT *m_mem_root;
+
+public:
+  Postponed_error_handler(MEM_ROOT *mem_root)
+    : m_first(nullptr), m_last(nullptr), m_mem_root(mem_root)
+  {}
+
+  bool handle_condition(THD *thd,
+                        uint sql_errno,
+                        const char *sqlstate,
+                        Sql_condition::enum_warning_level *level,
+                        const char *msg,
+                        Sql_condition **cond_hdl) override
+  {
+    /* Only capture errors, let warnings and notes pass through */
+    if (*level != Sql_condition::WARN_LEVEL_ERROR)
+      return false;
+
+    Error_entry *entry= (Error_entry*) alloc_root(m_mem_root,
+                                                  sizeof(Error_entry));
+    if (!entry)
+      return false;  // Can't store, let error propagate
+
+    entry->sql_errno= sql_errno;
+    strmake(entry->message, msg, sizeof(entry->message) - 1);
+    entry->next= nullptr;
+
+    if (m_last)
+      m_last->next= entry;
+    else
+      m_first= entry;
+    m_last= entry;
+
+    return true;
+  }
+
+  bool has_errors() const { return m_first != nullptr; }
+
+  void emit_errors()
+  {
+    for (Error_entry *e= m_first; e; e= e->next)
+      my_message_sql(e->sql_errno, e->message, MYF(0));
+  }
+
+  void clear()
+  {
+    m_first= m_last= nullptr;
+  }
+};
+
+
 /**
   This class is an internal error handler implementation for
   DROP TABLE statements. The thing is that there may be warnings during

sql/sql_rename.cc

@@ -20,6 +20,7 @@
 */
 
 #include "mariadb.h"
+#include "sql_class.h"
 #include "sql_priv.h"
 #include "unireg.h"
 #include "sql_rename.h"
@@ -51,6 +52,7 @@ static bool rename_tables(THD *thd, TABLE_LIST *table_list,
   the new name.
 */
 
+
 bool mysql_rename_tables(THD *thd, TABLE_LIST *table_list, bool silent,
                           bool if_exists)
 {
@@ -60,6 +62,7 @@ bool mysql_rename_tables(THD *thd, TABLE_LIST *table_list, bool silent,
   int to_table;
   const char *rename_log_table[2]= {NULL, NULL};
   DDL_LOG_STATE ddl_log_state;
+  Postponed_error_handler postponed_handler(thd->mem_root);
   DBUG_ENTER("mysql_rename_tables");
 
   /*
@@ -162,6 +165,15 @@ bool mysql_rename_tables(THD *thd, TABLE_LIST *table_list, bool silent,
     An exclusive lock on table names is satisfactory to ensure
     no other thread accesses this table.
   */
+
+  /*
+    Do not emit errors which may occur during the sequence of renamings,
+    because they will raise the 'thd->is_error()' flag, and `ddl_log_revert()`
+    may fail due to this. Instead, capture and collect errors and warnings
+    and emit them only after the renaming and possible reversion are complete.
+  */
+  thd->push_internal_handler(&postponed_handler);
+
   error= rename_tables(thd, table_list, &ddl_log_state,
                        0, if_exists, &force_if_exists);
 
@@ -192,15 +204,18 @@ bool mysql_rename_tables(THD *thd, TABLE_LIST *table_list, bool silent,
       my_ok(thd);
   }
 
+  thd->pop_internal_handler();
   if (likely(!error))
   {
     query_cache_invalidate3(thd, table_list, 0);
     ddl_log_complete(&ddl_log_state);
+    DBUG_ASSERT(!postponed_handler.has_errors());
   }
   else
   {
     /* Revert the renames of normal tables with the help of the ddl log */
     ddl_log_revert(thd, &ddl_log_state);
+    postponed_handler.emit_errors();
   }
 
 err: